This application relates to a turbine blade, wherein a tip cap for sealing off internal cooling passages has an improved purge hole arrangement, with two rows of purge holes.
Gas turbine engines typically include a plurality of sections acting in concert. Generally, a fan section delivers air into a compressor section. Air is compressed in the compressor section and delivered into a combustion section. The compressed air is mixed with fuel and combusted, and the products of combustion move downstream over a series of turbine rotors. The turbine rotors each include a plurality of blades, which are driven by the products of combustion to rotate the turbine rotors.
A good deal of design goes into the turbine blades. In particular, they are exposed to extremely hot temperatures. Internal cooling air passages are formed within the blades. The internal cooling passages are often serpentine, and circulate air from a radially inner location adjacent a platform, radially outwardly towards a tip of the blade, and then back toward the platform. The formation of these passages is facilitated if the tip of the blade is initially cast as an open end. Thus, the blade is typically cast with its end open, and a tip cap is later attached to close the end. The tip cap may be welded or brazed to the remainder of the blade body.
The tip caps are typically formed with a single row of purge holes. The purge holes allow some air from the cooling channels to escape outwardly and carry dirt. This removes the dirt from the cooling channels, where it otherwise might build up.
There are challenges with regard to the tip caps in that they have experienced field distress. As an example, there has been oxidation, cracking, bulging, etc. due to the high operating temperatures experienced by the tip caps. This becomes particularly acute in the first turbine blade row.